Flying cinder block in an abandoned building

The only IRL case I still can't explain. There's an unfinished building in my shithole town (it was there, a floor and a half left out of six, torn apart for building materials), where the whole alternative crowd used to hang out, hello, 2007, whatever. Back then not everyone even had ICQ, and calling each other wasn't really a thing either — whoever showed up, they entertain themselves however they can (tree line, all that). And so, autumn, October, maybe, around five in the evening, meaning it's still light out but it'll get dark soon, I come there, walked through all the floors, went up to the roof, the annex, the basement — nobody. Well, fuck it, I'm sitting in a window opening on the second floor, sucking down a 0.5 of Klinskoye, waiting, maybe someone'll show up. To picture the layout — a small lobby, on the left an annex like a gym or a cafeteria, opposite a lift shaft and stairs up/down, to the right a corridor with doorways into rooms. I'm sitting. Drinking. Not a sound. And I see how from the left, that is, from the gym, a fucking cinder block flies out, a hefty one, heavy, flies past me, flies nicely, smoothly like, and flies into the corridor on the right. I'm in shock, didn't come to my senses right away, looked out to check, but there were a fuckton of cinder blocks lying around in that corridor, whether the flying one was among them I never figured out. So what was that, anons? People, I remind you, there were none, I would've seen and heard them, bare concrete, footsteps echo for half a forest. The sound of the block falling, by the way, also wasn't there. If someone had thrown it, first of all it would've flown faster, second, well it wouldn't go in a straight line, fucking hell, gravity would pull it to the ground — what, have I never thrown cinder blocks, don't I know how they fly? I don't suffer from hallucinations, a 0.5 of beer and I didn't even finish it. Anyone got any thoughts on what that could've been, it's genuinely interesting to figure out? And yeah, I had a phone, even with a camera (0.3 MP, but beggars can't be choosers), and not even dead battery, and if that shit had been circling around me I'd have definitely filmed it, only it flew past once and fucked off, somehow the thought didn't come to me to whip out the camera and film, I was in shock O_o